Triarylmethane dyes and pigments are well-known in the art for providing various shades of blue coloration. These materials, such as those of the Spirit Blue family, are used primarily in inks and carbonless copy. The hue of these blue dyes and pigments can range from the violet (i.e., red shades) to blue-green (i.e., blue shades).
Triarylmethane dyes can be manufactured by first reacting a simple amino-substituted triarylmethane compound with an aromatic primary or secondary amine to form the principal chromophore, which is an aromatic amine-substituted triarylmethane. This reaction is usually conducted in solvent in the presence of an acid catalyst. This reaction is allowed to proceed until the reaction product composition has the desired hue, at which time the reaction is subdued. One way of subduing the reaction to achieve the desired hue control is to apply a vacuum to cool the reaction mixture and remove the solvent and any unureacted amine. As most of the solvent is removed, the temperature of the reaction mixture increases back up to the range of where it was before the vacuum was applied. The resulting molten organic glass is then cooled by any of a variety of means, after which it can be formed into solid particles for later use.
Depending on the cooling method used in the final step, the time required for cooling can vary significantly. In some processes, the molten product is cast onto a concrete floor, from where it can be broken up after it cools. In such a process, the cooling time is typically under one hour. Other processes involve cooling by passing the molten material over cooled rollers in a flaker, which can involve cooling times of 6-7 hours, or into drums, which can involve cooling times of 36-48 hours. Faster times (1 hour or less) are possible, but processing to achieve the desired flake characteristics of the finished product becomes more difficult, often requiring the addition of other components to maintain adequate fluidity during cooling.
In processes involving extended cooling times (e.g., .gtoreq.1 hour), it has now been discovered that side reactions can continue to occur. These side reactions can produce various yellow, orange, red, and brown colored species of indeterminate structure, which decreases the chroma and the tinctorial strength of the final material. It would thus be desirable to provide a method of manufacturing triarylmethane dyes and pigments of high purity and chroma.